Chemical reactions proceed at different rates. The determinants that affect reaction prices are:

surface area of a hard reactant concentration or press of a reactant temperature nature that the reaction presence/absence that a catalyst.

A readjust in one or more of these components may change the price of a reaction. In this lesson, friend will specify these factors, and describe and predict their effects on reaction rates.

Surface Area

Surface area is the exposed issue of a hard substance.

Imagine that you are holding a perfect cube the magnesium. The surface area is the sum of the area that all 6 sides the the cube. The surface ar area the the cube can be enhanced by splitting the cube into smaller cubes. Surface ar area is maximized when a single big cube is crushed to fine powder.

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The price of reaction of a solid problem is concerned its surface ar area. In a reaction in between a solid and also an aqueous/liquid/gas species, increasing the surface area the the solid-phase reactant boosts the variety of collisions per second and because of this increases the reaction rate.

In a reaction between magnesium metal and also hydrochloric acid, magnesium atoms have to collide through the hydrogen ions. Once the magnesium atoms form one large lump...


however, ...


the number of collisions per second between magnesium and also hydrogen is higher, and also the rate of reaction is faster.

Increasing the surface area the a hard reactant boosts the reaction rate.

By increasing surface area, over there are an ext collisions per unit of time. That"s why numerous solids room powdered utilizing a mortar and also pestle before being offered in a reaction.

Examples of various other reactions where surface ar area is important are:

active metals with acids, e.g. HCl through zinc charcoal dust v oxygen gas serial dust with oxygen gas


The concentration the a substance deserve to be to express in a variety of ways depending on the nature that a substance. Aqueous solutions generally have your concentrations expressed in mol/L. Because that example, a systems made by dissolving sodium hydroxide in water has its concentration expressed together moles the NaOH per litre the solution. Gases can likewise have their concentrations to express in mol/L.

In terms of the collision theory, raising the concentration the a reactant rises in the number of collisions in between the reacting species per 2nd and therefore increases the reaction rate.

Consider the reaction in between hydrochloric acid and zinc metal.



In one beaker, 6.00 mol/L HCl is reacted through 2.00 g that Zn.

In another,1.00 mol/L HCl is reacted v 2.00 g that Zn.

Which reaction should occur at the faster rate?

In regards to the collision theory, collisions between zinc atoms and also hydrochloric acid are more frequent in the maker containing6.0 M HCl - there is more acid every unit the volume.


You can adjust the concentration of an aqueous varieties by simply adding much more solute (to do it more concentrated) or adding much more solvent (to make it much more dilute).

You can change the concentration the a gas by adding more gas to a addressed volume or by decreasing the volume the the container. Whereas the concentration of a gas deserve to be diminished by remove (evacuating) a gas native a fixed volume or by enhancing the volume of the container.


The concentration the a gas is a role of the pressure on the gas. Increasing the press of a gas is specifically the very same as increasing its concentration. If you have a certain number of gas molecules, you deserve to increase the pressure by forcing them right into a smaller sized volume.


Under higher pressure or in ~ a higher concentration, gas molecule collide more frequently and also react in ~ a faster rate. Conversely, boosting the volume the a gas decreases push which subsequently decreases the collision frequency and thus reduces the reaction rate.

It is important to note yet that there room reactions including gases in i m sorry a pressure adjust does not affect the reaction rate. Because that this reason, the rates of reactions entailing gases have to be figured out by experiment.

Also note that solids and liquids room not influenced by push changes.

Need a great analogy because that the impact of concentration ~ above the price of a chemical reaction?


With the exception of part precipitation reactions involving ionic compounds in solution, just about all chemistry reactions take place at a quicker rate at higher temperatures. The question is why?

Temperature (in Kelvin degrees) is proportional come the kinetic energy of the corpuscle in a substance. Because that example, if the Kelvin temperature of a problem is doubled, climate the median kinetic energy of the particles in that substance is doubled.

At greater temperatures, particles collide much more frequently and with greater intensity.

Here"s an analogy.

Imagine the you room baby-sitting a bunch of 6 year olds. You put them in a yard and you let them run around. Every now and also then a pair of children will run into each other. Currently imagine the you decide to feed them part sugar. What happens? lock run approximately faster and of food there are many more collisions. Not only that, the collisions are likely to it is in a lot of harder/more intense.

Now, let"s look at the impact graphically. Recall the in any sample of matter (the example we offered previously was a gas), individual corpuscle have different kinetic energies. Some are moving rapid some are moving slowly, and also most are moving at part intermediate speed.


Increasing the temperature by say 10°C reasons some the the intermediate rate molecules to move faster. The result is more molecules with adequate kinetic energy to form an activated complicated upon collision!

Now consider the relationship in between threshold kinetic energy and also activation energy. Threshold kinetic power is the minimum amount of power required because that colliding particles to react - it is the indistinguishable of activation energy or the minimum potential power gain compelled to kind an triggered complex.

As you deserve to see top top the graph, a little increase in temperature can double the variety of molecules through the threshold kinetic energy.


Thus there are two impacts of increasing temperature: higher collision intensity and much more frequent collisions.

A general dominion is that a 10°C temperature boost can double a reaction rate. It turns out the the increase in the reaction rate is mostly a duty of the much more intense collisions. Increased collision frequency is not as far-ranging a factor.

Nature of Reactants

Individual nature of substances also affect reaction rates. The scope of this properties is vast and over there are few generalizations that you can apply consistently. Some of the nature in this classification are state the matter, molecule size, bond type and shortcut strength.

State of Matter

Gases have tendency to react much faster than solids or liquids: that takes power to different particles from each other. In order come burn candle wax, the hard wax has to be melted and also then vaporized before it reacts v oxygen. Methane gas is already in the gas state so the burns much faster than wax.



Aqueous ions tend to react faster than types in various other states the matter: solid lead(II) nitrate will react with solid potassium iodide, however the reaction is really, yes, really slow. That"s because the ionic bonding in each reactant is solid and the ions in each compound are tough to separate from every other. As soon as aqueous remedies of this compounds space mixed, the development of lead(II) iodide is rapid. In aqueous solutions, the ion of each compound room dissociated. When the two the solutions are combined together, all the is compelled for a reaction to take place is contact in between the lead(II) ions and the iodide ions.



Bond kind

Reactions including ionic varieties tend come proceed quicker than reactions entailing molecular compounds.


Bond strength

Reactions entailing the breaking of weaker bonds proceed much faster than reactions involving the break of more powerful bonds. Because that example, dual carbon come carbon bonds space stronger than solitary C-C bonds.



variety of Bonds/Molecular Size

Reactions involving the breaking of fewer bonds every reactant proceed quicker than those entailing the breaking of a larger number of bonds per reactant.


The an easy ion Fe2+ reacts quicker than oxalate (OOCCOO2-).

Kerosene burns an ext slowly 보다 methane due to the fact that there are much more bonds come be damaged per molecule that kerosene than there space per molecule that methane. Kerosene is a bigger molecule




A catalyst is a varieties that speeds up a chemical reaction without being chemically changed upon perfect of the reaction. In various other words, the massive of a catalyst is the very same before and also after a reaction occurs.

Common instances of catalysts include:

MnO2 in the decomposition the H2O2 Fe in the manufacture of NH3 Pt in the conversion of NO and CO to N2 and CO2

Recall that collisions only an outcome in reactions if the particles collide with enough energy to get the reactions began (i.e. To get rid of the activation energy barrier).

Also recall that activation energy coincides to threshold energy.


Only collisions including particles with sufficient kinetic energy an outcome in the formation of an triggered complex. Particles possessing much less than the threshold power simply bounce apart top top collision.

See more: What Does Fob Mean In Military ? Glossary: Forward Operating Base (Fob)

The number of successful collisions per unit the time be enhanced by lowering the threshold energy (or in regards to potential energy, lowering the activation energy).


Adding the suitable catalyst to a chemical device has exactly this impact on threshold/activation energy.

A catalyst provides an alternate pathway for the reaction - a pathway that has a reduced activation energy. Be cautious how you to speak it.


The catalytic analysis pathway (shown together a dotted green line above) has actually lower activation energy.

Relating this earlier to the kinetic power diagram, you check out that much more particles will certainly have adequate kinetic power to react. In other words, the addition of the catalyst increases the reaction rate.

You"ll discover the result of a catalyst additional on reaction price in the next lesson.


Textbook Readings web page 466: an approach for measure up Reaction prices web page 467: determinants That affect Reaction price pages 470-471: Collision Theory and also ... Concentration, surface Area, Nature the Reactants, and Temperature. Textbook exercise Items pages 467-468: items 1, 2, 4, 5, and also 6 web page 484: items 1 and also 2 pages 486-487: items 1, 2, 3, 4, 5, 6, 9, 12, and also 13 pages 538-541: items 12, 13, 28, 32, 34 and 35 an ext Practice item Why is kindling provided to begin a fire in a wood stove? think about this chemistry equation:
What impact would raising the temperature indigenous 25°C come 100°C have actually on the rate of this reaction? Explain. 10.0 g piece of zinc are included to 1.00 M and also 6.00 M hydrochloric acid services at the same time. Assuming over there is excess mountain in every container, i m sorry reaction will proceed faster? Explain. In regards to the effect of the nature of reactants on reaction rates, define the complying with observations. the reaction between perchloric acid and also iron is faster than the reaction in between nitrous acid and also iron. sulfur powder reacts gradually with silver, but sulfide ions are swiftly precipitated the end of equipment in a reaction v silver ions. barium reacts with water more readily than calcium methane burns an ext rapidly in air than kerosene (C14H30). Cane sugar (sucrose) can be hydrolysed to create two glucose molecules. This reaction is very slow.
If an acid is included to the reactants, the reaction price is much faster. What is the role of the acid? Explain.

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